The discovery of Haber and developments by Bosch of the reaction N2+3H2=2NH3 to produce ammonia was in relation to the World an epoch-making discovery and led to ammonia being one of the top tonnage chemicals in World production.
There is no doubt that without this discovery the burgeoning world population would have been subject to increased starvation.
The first commercial production of 20 metric tons of ammonia per day was by BASF in 1913. This enabled the Germans to produce nitrate explosives without the import of Chilean Saltpetre an important factor in World War I.
One of the pioneers in the subsequent development of the ammonia synthesis was the Italian company Ammonia Casale who have remained a world leader.
Casale recommended a synthesis pressure of 600 atm so the ammonia ex the reactor could be condensed without a refrigeration compressor. Post World War II ammonia plants tended to have a capacity of around 300 metric tons/day the limitation being the size of the reciprocating synthesis compressors which in general were horizontally opposed units.
In Wyoming for example these plants were considered rather like gas stations serving an agricultural community of around 250-mile radius curve from the ammonia production. In 1954 Torresy and Hamilton produced designs for skid mounted units of 100 and 200 short tons/day of ammonia. These plants had horizontally opposed reciprocating synthesis gas driven by synchronous electric motors. Specific consumption in thermally equivalent gas was 50 MM BTU/metric ton of ammonia. Some 30 of these plants which were fabricated by Krupp in Germany and Voest in Austria were sold worldwide and some are still operating including one in Sudan which was never started up because the Sudanese government did not supply the gas. Commercially these plants were a success at the time because the buyer had only to provide the civil work for the foundations and the need for mechanical erection was eliminated.
In the 1960's the M.W. Kellogg Company opened the era of mega-ammonia plants with a radical new design. This design involved raising steam from the primary and secondary reformer to supply steam turbines driving the centrifugal synthesis gas, recycle and refrigeration compressors and reducing the ammonia synthesis pressure to between 140 and 160 atm. Gas consumption was reduced to around 30 MMBTU/metric ton of ammonia with the plant having minimal electricity consumption. The centrifugal compressors opened the way to increased flows and consequently higher ammonia capacity. The first plant to utilize the process was the Mississippi Chemical Corporation with a capacity of 1000 metric tons/day. However, the physical limitations of centrifugal compressors meant it was not possible to design ammonia plants with a capacity of or below 500 metric tons/day.
For this development M.W. Kellogg received the prestigious 1967 Kirkpatrick Chemical Engineering Award. In Van Nostrand's Scientific Encyclopedia Eighth Edition a Reference 1 this is described and the following statements made
“Most ammonia plants built since early 1960s in the 600-1500 short tons of ammonia per day are based on the new integrated process”
“One of the major factors contributing to the improved economics of ammonia plant is the application of multistage centrifugal compressors which have replaced reciprocating compressors traditionally used in the synthesis feed and recycle service by a single centrifugal compressor”
“Developments have been centered around the 1960s basic process scheme with modifications to improve efficiency therefore the basic process steps have not changed in any major way”
The first statement of a lower limit of 600 short tons a day of ammonia was because this was the lower limit of the recycle wheel in the centrifugal compressor in this process design.
Until today ammonia plants of this lower capacity have used reciprocating compressors for the synthesis and recycle duty. Reciprocating compressors are expensive and require frequent maintenance.
The cost of ammonia production is largely based on two factors, the price of gas and the capital charges.
New ammonia plants producing 2000 metric tons of ammonia per day with an accompanying urea plant can cost around $1 billion and face major problems in implementation. Financiers cannot often obtain adequate information on the security of the market. The plants are often projected in areas where the field construction is difficult and the cost uncertain. Buyers normally want turnkey plants. This compels the contractor to include high levels of profit and contingency to cover the risk.
This all points to the need to develop small economic ammonia plants which can be situated in countries where the fertilizer consumption per unit area is low and also in countries where cheap fracked gas is available such as the United States.
Small ammonia plants will not succeed unless their gas consumption per metric ton of ammonia is equivalent to that of a major scale plant and further their capital cost is pro-rata to that of the larger plant.
It therefore may be desired for a process method of removing this bottleneck and lowering the cost of ammonia plants. Two recent improvements have contributed to this ability. Improved ammonia synthesis catalysts lead to the ability to synthesize ammonia at a pressure between 70-120 bar. Concurrently in 2009 KOBELCO, Japan developed the first screw compressors capable of a delivery pressure of 100 bar. Previously screw compressors which were widely used had a maximum delivery pressure of 66 bar.